A Galilean telescope can form an upright virtual image 1030a of an observed object 1030 and change an included angle from the virtual image to eyes by using a convex lens 1010 and a concave lens 1020, so as to achieve a visual effect of drawing near or pushing away the observed object along an optical axis 1040. The magnification factor can be changed and focusing can be implemented by adjusting focal lengths of the two lenses and a distance between the lenses, as shown in FIG. 17a to FIG. 17c. 
A lens with a fixed focal length has found wide applications in optical devices such as glasses, telescopes, cameras, and microscopes, and by combining lenses of different focal lengths and adjusting a distance between the lenses, a focal length can be dynamically adjusted for a lens group. In addition, for new-type lenses with an electronically adjustable focal length, the focal length of a single lens can also be dynamically adjusted.
Wearable devices such as Google glass and smartwatches are gradually accepted by people, and these electronic smart devices will make people's life more and more convenient.
When a user watches or records an image of an object, a perspective deformation may occur on a received image of the object relative to an original image of the object in a case where the user is not right in front of the object. If the foregoing perspective deformation can be directly adjusted during imaging through imaging lenses, an image with no perspective deformation or a slight degree of perspective deformation of an object can be directly obtained, thereby greatly improving user experience.